Image sensors are electronic integrated circuits that can be used to produce still or video images. Solid state image sensors can be, for example, of the charge coupled device (“CCD”) type or the complementary metal oxide semiconductor (“CMOS”) type. Either type of image sensor includes a two-dimensional array of pixels, wherein each pixel is a semiconductor device that transforms incident light photons into an electrical current signal. Applications for image sensors include cell phones, digital cameras and camcorders, webcams, automotive and medical equipment, and security cameras.
Image sensors used in automotive, medical and surveillance cameras are typically small, low voltage, low power consumption sensors that support analog composite video output and are capable of directly interfacing with a video cassette recorder (“VCR”), a television (“TV”) or a monitor. When it comes to analog video communication, it is notable that different regions in the world have adopted different video/TV standards; accordingly, products targeting a specific region must meet the local standard. The two most common video standards today are generally referred to as National Television System Committee (“NTSC”) and Phase Alternating Line (“PAL”). NTSC uses a refresh rate of 29.97 frames per second, each frame consisting of 525 scan lines, of which only 480 are arranged as a visible raster, and carry the picture content. The remaining lines are within the vertical blanking interval, and may be used for synchronization, closed captioning and other non-imagery information. PAL, on the other hand, uses a refresh rate of 25 frames per second and a total of 625 lines per frame, 576 of which are dedicated to picture content. Some applications may use low-resolution versions of NTSC and PAL, for example using only 240 visible lines in NTSC, and 288 visible lines in PAL. A line time is the time allocated to displaying each scan line, which for NTSC is 1/(29.97*525) second. Each line time includes a horizontal blanking interval, typically used for synchronization, as well as time allocated for displaying each pixel of the image. A third common analog video standard, Sequential Color With Memory (translated from the French Séquentiel couleur à mémoire) (“SECAM”), typically used for example in France and Russia, resembles PAL in that it also uses a refresh rate of 25 frames (50 fields) and 625 lines per frame.